PM6685 STMicroelectronics, PM6685 Datasheet - Page 36

• Manufacturer Part Number: PM6685
• Description: IC CTLR DUAL SYNC STDN 5X5VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6685

• Applications: Controller, Notebook Power System
• Voltage - Input: 6 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: -3.3V, 5V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5 V, 3.3 V
• Output Current: 0.1 A
• Input Voltage: 5.5 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 10 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Monitoring and protections
36/48
Equation 24
Due to the capacitive divider (CINT, Cfilt), the ripple voltage at the COMP pin is given by:
Equation 25
Where VRIPPLEout is the output ripple and q is the attenuation factor of the output ripple.
If the ripple is very small (lower than approximately 30 mV), a further compensation network,
named virtual ESR network, is needed. This additional part generates a triangular ripple
that is added to the ESR output voltage ripple at the input of the integrator network. The
complete control schematic is represented in
Figure 37. Virtual ESR network
The T node voltage is the sum of the output voltage and the triangular waveform generated
by the virtual ESR network. In fact the virtual ESR network behaves like a further equivalent
ESR RESR.
A good trade-off is to design the network in order to achieve an RESR given by:
Equation 26
V
RIPPLE
INT
Doc ID 11674 Rev 8
=
R
INT
V
RIPPLEout
R
=
ESR
2
π
=
×
×
V
f
CUT
RIPPLE
C
Δ
Figure 37
INT
I
L
×
C
1
INT
C
C
+
INT
−
INT
C
R
filt
out
×
+
.
=
C
C
filt
filt
V
RIPPLEout
×
q
PM6685